This invention relates to amplifiers and more particularly to the dynamic biasing thereof.
As is well known, the bias current at the drain of a field effect transistor (FET) is a function of the bias voltage at the gate thereof. Likewise, the bias current at the collector of a bipolar transistor is a function of the bias voltage at the base thereof. The bias voltage determines the bias current.
Linearity is important in high frequency applications and significant bias current is required to maintain FETs in their linear response region. Thus Class A amplifiers are efficient at high power settings but inefficient at low power settings because of the high bias current. Class C amplifiers which have a low quiescent bias current are more efficient, but suffer from intermodulation and harmonic distortion. Thus, amplifiers with a fixed bias current as determined by a fixed bias voltage are compromises between efficiency on the one hand and the linearity and distortion performance of the amplifier on the other hand.
Accordingly, it is an object of the present invention to provide a novel amplifier and method in which the bias voltage of the amplifier, and thus the bias current, is dynamically varied as a function of the required output power of the amplifier.
It is another object of the present invention to provide a novel amplifier and method for improving the efficiency of a Class A amplifier.
It is another object of the present invention to provide a novel amplifier and method for improving the performance of a Class C amplifier.
It is yet another object of the present invention to provide a novel amplifier and method of dynamically controlling the bias of an amplifier.
It is still another object of the present invention to provide a novel amplifier and method of controlling the bias voltage of an amplifier as a function of the modulation envelope of the signal to be amplified.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.